1. Field of the Invention
The present invention relates to a remote communication system, especially a remote communication system that remotely executes data read/write of all control units through a network.
2. Description of Prior Art
Recent communication port structures are categorized into parallel port and serial port. Theoretically the transmission speed of serial port is slower than that of parallel port; however, serial port is widely used in consumer products, electronic products, industrial products and communication products because of its simple structure, easy connection, long transmission distance, high noise immunity and low cost. Especially in industrial environment, serial port is the best choice for connecting numerous remote control units to a network, and the mostly used function block is universal asynchronous receiver/transmitter (UART). UART transmits digital data at a fixed Baud rate and defines data frames with a start bit and a stop bit. A parity bit can be added to increase the reliability of transmission. Therefore, transmitting an 8-bit data requires 11 bit time units, including start bit, stop bit and parity bit.
FIG. 1 shows a traditional connecting method and system of a serial port using universal asynchronous receiver/transmitter (UART). The system comprises a plurality of control units 10. Each control unit 10 includes an analog/digital converter 20 and a microcontroller 30 with a universal asynchronous receiver/transmitter (UART) 301 therein. The universal asynchronous receiver/transmitter (UART) contains a receiver 302 and a transmitter 303. The feature of this connecting method and system is that all the receivers 302 of control units 10 on the same network are connected with the transmission terminal 40 to form a common receiving node. The transmitters 303 connect to the response terminal 50 and form a common transmitting node. When transmission terminal 40 sends a signal, all control units 10 receives this signal simultaneously. Therefore, each control unit 10 must have a unique and non-repeating address and the received message frames must include at least one byte of address information for calling a corresponding control unit 10. Then the control unit 10 being called starts to execute the command it receives, and sends a response message to the common transmitting node. Other control units 10 must turn off their transmitters to prevent from signal collision if more than one signals are sharing the transmission terminal 40.
The technique described above is widely used in the products those execute remote control through the network, especially those using RS-485, RS-422 or other similar standard interfaces or communication protocols to implement the communication function of the system. These communication methods are simple but with the following drawbacks:
1. Each control unit in the same system must set a fixed and non-repeating address. It is very inconvenient when building and maintaining a system. The communication function fails if the address information is altered intentionally during usage, increasing the loading of managing the system.
2. Only one control unit is allowed to respond at one time, hence signals have to be send individually to each control unit. The communication efficiency drops with an increase in the number of control units in a system.